Printing systems

ABSTRACT

The present disclosure is drawn to printing systems. In one example, a printing system can include a pretreatment head, an inkjet print head, and a post-treatment head. The pretreatment head can include a first plasma generator to apply a plasma treatment to a media substrate. The inkjet print head can be positioned with respect to the pretreatment head to form a printed image on the media substrate after the plasma treatment. The post-treatment head can include a second plasma generator positioned with respect to the inkjet print head to treat the printed image on the media substrate.

BACKGROUND

Inkjet printing often utilizes ink that includes a colorant, such as apigment, dispersed in a liquid ink vehicle. One challenge oftenencountered with this type of ink is obtaining high color saturation andoptical density of images printed with the ink. When the ink is printedon plain paper, the liquid vehicle can be absorbed into the paper. Thecolorant can thus be transported with the liquid vehicle into the paper.Because a portion of the colorant is absorbed below the surface of thepaper, the printed image may appear washed out, having a low colorsaturation or optical density. Other problems encountered when printinginkjet inks on plain paper include strike through (e.g., ink may bevisible on the non-printed side of the paper), poor edge quality,mottling, and inter-color bleeding. Improving image quality can occur byreducing the negative visual impact of one or more of these problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional top view of an example surfacebarrier discharge plasma generator in accordance with examples of thepresent disclosure.

FIG. 1B is a schematic cross-sectional end view of an example surfacebarrier discharge plasma generator in accordance with examples of thepresent disclosure.

FIG. 2A is a schematic side view of an example printing system inaccordance with examples of the present disclosure.

FIG. 2B is a schematic top view of an example printing system inaccordance with examples of the present disclosure.

FIG. 3 is a schematic side view of an example printing system inaccordance with examples of the present disclosure.

FIG. 4 is a schematic top view of an example printing system inaccordance with examples of the present disclosure.

FIG. 5 is a flowchart illustrating an example method of forming adurable printed image on a media substrate in accordance with examplesof the present disclosure.

FIG. 6 is a schematic cross-sectional side view of an example printedarticle in accordance with examples of the present disclosure.

FIG. 7 is a schematic cross-sectional side view of an example printedarticle in accordance with examples of the present disclosure

DETAILED DESCRIPTION

The present disclosure is drawn to printing systems employing inkjetinks to print an image on a media substrate and dual plasma generatorsincorporated in the printing system. A first plasma generator can beused to pretreat a media substrate before printing, and a second plasmagenerator can be used to treat the printed image after printing.

The plasma pretreatment can modify the surface of the media substrate sothat the surface interacts with inkjet ink printed on the surface toimprove print quality. In one example, applying a plasma pretreatment toplain paper, even without the use of fixer present (e.g., a digitallyprinted fixer or an analog fixer coating, such as in ColorLok® paper),can provide a paper substrate that can meet or exceed the print qualityachieved using paper with a fixer. For example, the print quality on aplain paper, after plasma pretreatment, can approach, match, or exceedthe print quality provided using ColorLok® paper or paper that has afixative solution applied before printing.

The second plasma generator can be used to treat the printed image. Insome examples, the inkjet ink can include a plasma curable component,such as a binder, which can be cured by the plasma treatment. Forexample, a curable binder can include monomers, oligomers, or polymersthat polymerize or crosslink upon exposure to free radicals. The plasmagenerator can generate free radicals, which interact with the curablebinder to begin the polymerization or crosslinking process. In otherexamples, the second plasma generator can be used in conjunction with apolymerizable overcoat composition. The polymerizable overcoatcomposition can be injected into the plasma generated by the secondplasma generator. Thus, the overcoat composition can polymerize on theprinted image and form a protective overcoat over the image.

A variety of types of plasma generators may be used in the printingsystems according to the present technology. In some examples, the firstand/or second plasma generator described above can be a surface barrierdischarge plasma generator. This particular type of plasma generator isa type of dielectric barrier discharge plasma generator, and includeselectrodes located beneath a surface of a dielectric material. Theelectrodes can be separated from each other and from the media substrateby the dielectric material. A high voltage alternating current can beapplied across the electrodes to form diffuse plasma arcs on the surfaceof the dielectric material. FIGS. 1A-1B show an example of a surfacebarrier discharge plasma generator 100 having a first electrode 105 anda second electrode 110 embedded in a dielectric plate 115. FIG. 1A showsa top cross-sectional view. A power supply 120 applies a potentialdifference across the first electrode and second electrode. FIG. 1Bshows an end cross-sectional view. Plasma arcs 125 can form along thesurface 130 of the dielectric plate.

In certain examples, the surface barrier discharge plasma generator canbe a coplanar surface barrier discharge plasma generator. For example,the electrodes can be oriented in a common plane beneath the surface ofthe dielectric material. The surface of the dielectric material can be aflat planar surface. In other examples, the dielectric material can havea curved or other shape, and the electrodes can be oriented beneath thesurface to conform to the shape of the surface. For example, theelectrodes can be located at an approximately uniform distance beneaththe surface.

In some examples, the power supply can provide a high voltagealternating current. In certain examples, the surface barrier dischargeplasma generator can be operated at a voltage from 1 kV to 30 kV. Infurther examples, the high voltage alternating current can have afrequency from 1 kHz to 500 kHz. In one example, the surface barrierdischarge plasma generator can be a plasma generator available fromROPLASS S.R.O., such as the RPS40, RPS400, or RPS25x plasma systems.

In some examples, both the first and second plasma generators in theprinting system can be surface barrier discharge plasma generators. Insuch examples, a single power supply can be used to power both plasmagenerators. The power supply can provide the appropriate voltages andfrequencies for the plasma generators to form stable plasma arcs.

As shown in FIG. 1B, the first electrode 105 and second electrode 110may be oriented in a common plane embedded within the dielectric plate115. The plasma arcs 125 may be confined to a volume close to thesurface 130 of the dielectric plate. For this reason, the plasma arcs inthis example can be referred to as a “surface dielectric barrierdischarge” which can be generated from a “surface barrier dischargeplasma generator” described herein. This is different from a plasmagenerator that generates a volumetric dielectric barrier discharge.Volumetric dielectric barrier discharge occurs in a volumetric spacebetween two electrodes, rather than from a common surface. In volumetricdielectric barrier discharge plasma systems, electrodes may be orientedin parallel planes, such as two parallel plate electrodes with adielectric barrier between the electrodes in the space between theelectrodes from two different surfaces. Thus, plasma arcs form in thevolume between the electrodes.

However, in the surface barrier discharge plasma generator 100 shown inFIG. 1B, the plasma arcs occur along a surface that is common to bothelectrodes of the dielectric plate. This plasma tends to be morehomogenous and has a higher energy density than volumetric dielectricbarrier discharge plasma. That being described, either type of plasmatreatment can be used.

In some examples, the plasma generated by the coplanar dielectricbarrier discharge plasma generator can have a depth from 0.1 mm to 5 mm.In other words, the plasma can extend to a distance of 0.1 mm to 5 mmfrom the surface of the dielectric plate. In further examples, theplasma can have a depth from 0.2 mm to 2 mm or from 0.5 mm to 1 mm. Theplasma can have a high energy density, for example from 50 W/cm³ to 250W/cm³. In further examples, the plasma can have an energy density from75 W/cm³ to 200 W/cm³ or from 80 W/cm³ to 150 W/cm³. In terms of surfacearea of the media substrate being treated, the energy density of theplasma can be from 0.5 W/cm² to 250 W/cm², from 1 W/cm² to 50 W/cm², orfrom 2 W/cm² to 10 W/cm², in some examples.

The plasma generated by the surface barrier discharge plasma generatorcan be “cold” plasma. For example, the plasma can have a temperature ofless than 50° C. Thus, the plasma can safely be used to treat mediasubstrates such as paper without damaging the substrates due to hightemperatures.

In further examples, the surface barrier discharge plasma generator canoperate at atmospheric pressure in an atmosphere of normal air. Unlikesome other types of plasma generators, surface barrier discharge plasmagenerators in some cases do not require reduced pressure or any specialgas flow to operate. For example, some other types of plasma generatorsemploy high gas flows to blow a plasma arc out of a nozzle. The gasrequired for these systems in some cases includes noble gases such asArgon or Helium. In contrast, the surface barrier discharge plasmagenerators described herein can be used at normal atmosphericconditions.

In some examples, the surface barrier discharge plasma generator canmodify the surface of the media substrate so that the surface hasimproved interactions with inkjet ink. Specifically, the first plasmagenerator can modify the surface of media substrate prior to printing animage using the inkjet print head. This plasma pretreatment can resultin better print quality of the printed image. Without being bound to aparticular mechanism, the plasma treatment can produce highly oxidizingspecies such as atomic oxygen and OH radicals. These species can reactwith components in the media substrate to form oxygen-containing groupssuch as —OH groups and carbonyl groups. In certain examples, the plasmatreatment can modify the surface of the media substrate withoutsignificantly changing the pH of the surface. In other words, the plasmatreatment can modify the surface by forming certain oxygen-containinggroups, but without forming a substantial quantity of acid groups on thesurface.

In further examples, the surface barrier discharge plasma generator canalso have the effect of forming cationic species in the surface of themedia substrate, depending on the type of media substrate used. Forexample, many types of paper contain calcium carbonate, which is addedwhen the paper is manufactured. The plasma treatment can in some casesconvert the calcium carbonate into calcium ions. For example, thecalcium carbonate can in some examples react to form Ca²⁺ and CO₂. Infurther examples, the calcium carbonate can react via a series ofreactions with nitrogen in the air to form calcium nitrate. Unlikecalcium carbonate, which is insoluble in water, calcium nitrate issoluble in water and can supply Ca²⁺ ions when an aqueous ink is printedon the surface. The Ca²⁺ ions can act as a fixer when the ink is printedon the surface. In still further examples, the media substrate mayinclude other components that can be converted into cationic species bythe plasma treatment. Regardless of whether these chemical reactionsoccur or not in each and every case, irrespective of the variouspossible mechanisms, it has been observed that print quality can beimproved on a wide variety of papers using the surface barrier dischargeplasma generators as described herein.

In other examples, printing systems according to the present technologycan employ other types of plasma generators to treat images printed onmedia substrates. In one example, the plasma generator can includeparallel plate plasma with electrodes located on both sides of the mediasubstrate. A dielectric layer can also be positioned between theelectrodes. Plasma can form in the volume between the electrodes when ahigh voltage, high frequency current is applied to the electrodes.

With this description in mind, FIG. 2A shows a schematic side view of aprinting system 200 in accordance with examples of the presentdisclosure. The printing system includes inkjet print heads 230, 231,232, 233. The inkjet print heads are positioned to print an image on amedia substrate 220. The inkjet print heads can be used to printdifferent colors, such as cyan, magenta, yellow, black, blue, green,red, purple, orange, gray, etc. In certain examples, the colors may becyan, magenta, and yellow (three colors); or cyan, magenta, yellow, andblack (four colors). The inkjet print heads may also be in fluidcommunication with ink reservoirs 240, 241, 242, 243, and may carry theinks. The media substrate, as shown, can be conveyed past thepretreatment head and the inkjet print heads by conveyors 250. Apretreatment head 210 including a first plasma generator can bepositioned with respect to the inkjet print heads to pretreat the mediasubstrate before the inkjet print heads print the image onto the mediasubstrate. A post-treatment head 215 including a second plasma generatorcan be positioned to treat the printed image after the image has beenapplied to the media substrate.

As shown in FIG. 2A, the inkjet print heads 230, 231, 232, and 233 andplasma generators can be positioned a small distance above the surfaceof the media substrate 220. The inkjet print heads can be positioned ata distance typically used in inkjet printing. In various examples, theplasma generators can be positioned over a range of distances from themedia substrate. In one example, the plasma generators can be positionedup to 10 mm from the surface of the media substrate. For example, theplasma generators can be from 0.1 mm to 10 mm from the surface of themedia substrate. Depending on the distance of the plasma generators fromthe media substrate, the media substrate can be within the plasma arcsor beneath the plasma arcs. In some examples, media substrate and theprinted image on the media substrate can be effectively treated eitherwithin the plasma arcs or beneath the plasma arcs. In further examples,the plasma generator can be fixed at a distance from the mediasubstrate, or moveable with respect to the media substrate so that thedistance can be adjusted.

In some examples, the first and/or second plasma generator can be indirect contact with the media substrate. In a further example, the firstplasma generator can be in direct contact with the media substrate topretreat the media substrate, but the second plasma generator can bepositioned a distance away from the media substrate to avoid rubbing orsmudging the printed image.

FIG. 2B shows a schematic top view of the printing system of FIG. 2A. Asshown in FIG. 2B, the inkjet print heads 230, 231, 232, 233 and plasmagenerators 210 and 215 can have nearly the same width as the mediasubstrate 220. In certain examples, the plasma generators can be 75% ormore as wide as the media substrate, or 90% or more as wide as the mediasubstrate. In further examples, the plasma generators can be as wide asthe media substrate or wider.

In some examples, the inkjet print heads and plasma generators can beheld stationary while the media substrate is conveyed past. Thus, in oneexample, the plasma generators can plasma treat the entire width of themedia substrate or a portion of the media substrate as wide as theplasma generators. In other examples, it may be that the plasmagenerators and/or the inkjet print heads may also be movable on acarriage and traverse the media substrate. In other words, in theexample shown, these features are static, but they may alternatively bemovable.

In some examples, the first and second plasma generators can bepositioned at a distance from the inkjet print heads. The plasmapretreatment applied by the first plasma generator can effectivelymodify the surface of the media substrate very quickly, so that distancebetween the pretreatment plasma generator and the inkjet print heads isnot particularly limiting, e.g., many different distances can be used.Additionally, the plasma treatment can retain its effect on the surfaceof the media substrate for an extended time, such as more than one monthor more than one year. Thus, no particular proximity of distance or timebetween use of the pretreatment head and the inks impact the result.However, in some examples, the pretreatment head can be positioneddirectly adjacent to the inkjet print heads. In other examples, thepretreatment head can be positioned any convenient distance from theinkjet print heads, such as from 1 mm to 10 meters away from the inkjetprint heads. This can provide advantages over printing systems thatapply a liquid fixer solution to a media substrate before printing,because such systems often employ a drying zone between the fixerapplication and the print heads. Such systems can use a drying oven or along distance between the fixer application and the print heads to allowwater and/or other solvents in the fixer solution to evaporate. In somecases, such printing systems run at a slower printing speed to give thefixer solution more time to dry. In contrast, the plasma treatment usedin the present technology can be a dry treatment. Therefore, in manyexamples, no liquid is added to the media substrate and no drying zoneis used between the pretreatment head and the inkjet print heads.

The distance between the inkjet print heads and the second plasmagenerator can be sufficient to allow the printed image to partially orfully dry before the image is plasma treated. In some examples, acurable inkjet ink can produce a stronger cure when the ink has beenallowed to dry. However, other inks may produce a stronger cure if theyare cured when still wet. Thus, the position of the plasma generator canbe selected based on the characteristics of the ink being employed. Infurther examples, the printing system can include a dryer or drying zonebetween the inkjet print heads and the plasma generator. The dryer ordrying zone can dry the ink making up the printed image more quickly.For example, a dryer can include a heater to heat the printed image toevaporate water and/or volatile solvents in the ink.

It should be noted that the example shown in FIGS. 2A and 2B is only asingle example of the presently disclosed technology. In other examples,printing systems according to the present disclosure can have a varietyof different configurations. FIG. 3 shows another example of a printingsystem 300 that includes inkjet print heads 330, 331, 332, 333 in fluidcommunication with ink reservoirs 340, 341, 342, 343. A pretreatmenthead 310 and post-treatment head 315 including plasma generators arepositioned before and after the inkjet print heads, respectively. Thesecomponents are positioned to print on a first surface of the mediasubstrate 320 and plasma treat the media substrate and the printedimage. Another set of inkjet print heads 330′, 331′, 332′, 333′ in fluidcommunication with ink reservoirs 340′, 341′, 342′, 343′ and anotherpretreatment head 310′ and post-treatment head 315′ are positioned on anopposite side of the media substrate to print and treat the oppositesurface of the media substrate.

The media substrate is conveyed between the two sets inkjet print headsand plasma generators by conveyors 350. Thus, the system can pretreat,print, and post-treat on both surfaces of the media substratesimultaneously.

In other examples, the plasma generators and/or the inkjet print headcan be movable with respect to the media substrate. For example, in aweb fed printing system the plasma generators and/or inkjet print headcan move in a direction perpendicular to the movement direction of themedia web. In another example, the printing system can be sheet fed. Amedia substrate sheet can be fed by conveyors past the plasma generatorsand inkjet print head, while the plasma generators and/or inkjet printhead can move in a direction perpendicular to the movement direction ofthe media sheet. In a further example, the printing system can have astatic printing bed on which a media substrate sheet is placed. Theplasma generators and/or the inkjet print head can move in twodimensions (i.e., the x-axis and y-axis directions) over the mediasubstrate sheet to pretreat the media substrate sheet, print on themedia substrate sheet, and post-treat the printed image.

FIG. 4 shows an example of a printing system 400 including a stationarymedia substrate sheet 420. In this system, a first plasma generator 410,inkjet print heads 430, 431, 432, 433, and a second plasma generator 415are located together on a carriage 460. The carriage is moveable in thex-axis and y-axis directions. The first plasma generator can pass overan area of the media substrate sheet first to pretreat the area, andthen inkjet print heads can pass over the pretreated area to print animage on the pretreated area. Finally, the second plasma generator canpass over the printed image to post-treat the printed image.

As mentioned above, the printing systems described herein can include aninkjet print head. In some examples, a printing system can include asingle inkjet print head. The inkjet print head can be in fluidcommunication with a reservoir of black ink or a colored ink. In otherexamples, the printing system can include multiple inkjet print heads.For example, the printing system can include an inkjet print head forseveral different colors, such as cyan, magenta, yellow, and black. Infurther examples, other colors of ink can be included.

As used herein, “inkjetting” or “jetting” refers to ejectingcompositions from jetting architecture, such as inkjet architecture.Inkjet architecture can include thermal, piezo, or continuous inkjetarchitecture. A thermal inkjet print head can include a resistor that isheated by electric current. Inkjet ink can enter a firing chamber andthe resistor can heat the ink sufficiently to form a bubble in the ink.The expansion of the bubble can cause a drop of ink to be ejected from anozzle connected to the firing chamber. Piezo inkjet print heads aresimilar, except that instead of a thermal resistor, a piezoelectricelement is used to mechanically force a drop of ink out of a nozzle. Ina continuous inkjet printing system, a continuous stream of ink dropletsis formed and some of the droplets can be selectively deflected by anelectrostatic field onto the media substrate. The remaining droplets maybe recirculated through the system. Inkjet print heads can be configuredto print varying drop sizes such as less than 10 picoliters, less than20 picoliters, less than 30 picoliters, less than 40 picoliters, lessthan 50 picoliters, etc.

In some cases, the ink used in the printing systems described herein canbe a water-based inkjet ink or a solvent-based inkjet ink. Inkjet inksgenerally include a colorant dispersed or dissolved in an ink vehicle.As used herein, “liquid vehicle” or “ink vehicle” refers to the liquidfluid in which a colorant is placed to form an ink. A wide variety ofink vehicles may be used with the methods of the present disclosure.Such ink vehicles may include a mixture of a variety of differentagents, including, surfactants, solvents, co-solvents, anti-kogationagents, buffers, biocides, sequestering agents, viscosity modifiers,surface-active agents, water, etc.

Generally the colorant discussed herein can include a pigment and/ordye. As used herein, “dye” refers to compounds or molecules that impartcolor to an ink vehicle. As such, dye includes molecules and compoundsthat absorb electromagnetic radiation or certain wavelengths thereof.For example, dyes include those that fluoresce and those that absorbcertain wavelengths of visible light. In most instances, dyes are watersoluble. Furthermore, as used herein, “pigment” generally includespigment colorants, magnetic particles, aluminas, silicas, and/or otherceramics, organo-metallics or other opaque particles. In one example,the colorant can be a pigment.

In certain examples, the colorant can be a pigment having a dispersinggroup covalently bonded to surfaces of the pigment. The dispersinggroups can be, for example, small groups, oligomeric groups, polymericgroups, or combinations thereof. In other examples, the pigment can bedispersed with a separate dispersant. Suitable pigments include, but arenot limited to, the following pigments available from BASF: Paliogen®Orange, Heliogen® Blue L 6901 F, Heliogen® Blue NBD 7010, Heliogen® BlueK 7090, Heliogen® Blue L 7101 F, Paliogen® Blue L 6470, Heliogen® GreenK 8683, and Heliogen® Green L 9140. The following black pigments areavailable from Cabot: Monarch® 1400, Monarch® 1300, Monarch® 1100,Monarch® 1000, Monarch® 900, Monarch® 880, Monarch® 800, and Monarch®700. The following pigments are available from CIBA: Chromophtal® Yellow3G, Chromophtal® Yellow GR, Chromophtal® Yellow 8G, Igrazin® Yellow 5GT,Igralite® Rubine 4BL, Monastral® Magenta, Monastral® Scarlet, Monastral®Violet R, Monastral® Red B, and Monastral® Violet Maroon B. Thefollowing pigments are available from Degussa: Printex® U, Printex® V,Printex® 140U, Printex® 140V, Color Black FW 200, Color Black FW 2,Color Black FW 2V, Color Black FW 1, Color Black FW 18, Color Black S160, Color Black S 170, Special Black 6, Special Black 5, Special Black4A, and Special Black 4. The following pigment is available from DuPont:Tipure® R-101. The following pigments are available from Heubach:Dalamar® Yellow YT-858-D and Heucophthal Blue G XBT-583D. The followingpigments are available from Clariant: Permanent Yellow GR, PermanentYellow G, Permanent Yellow DHG, Permanent Yellow NCG-71, PermanentYellow GG, Hansa Yellow RA, Hansa Brilliant Yellow 5GX-02, HansaYellow-X, Novoperm® Yellow HR, Novoperm® Yellow FGL, Hansa BrilliantYellow 10GX, Permanent Yellow G3R-01, Hostaperm® Yellow H4G, Hostaperm®Yellow H3G, Hostaperm® Orange GR, Hostaperm® Scarlet GO, and PermanentRubine F6B. The following pigments are available from Mobay: Quindo®Magenta, Indofast® Brilliant Scarlet, Quindo® Red R6700, Quindo® RedR6713, and Indofast® Violet. The following pigments are available fromSun Chemical: L74-1357 Yellow, L75-1331 Yellow, and L75-2577 Yellow. Thefollowing pigments are available from Columbian: Raven® 7000, Raven®5750, Raven® 5250, Raven® 5000, and Raven® 3500. The following pigmentis available from Sun Chemical: LHD9303 Black. Any other pigment and/ordye can be used that is useful in modifying the color of the ink.Additionally, the colorant can include a white pigment such as titaniumdioxide, or other inorganic pigments such as zinc oxide and iron oxide.

In further examples, the ink can include a binder. In some examples, thebinder can be a latex polymer. In further examples, the binder caninclude polymers, copolymers, or combinations thereof. The polymers andcopolymers can be formed of styrene, acrylic acid, methacrylic acid,methyl methacrylate, butyl acrylate, divinylbenzene, or combinationsthereof. In another example, the binder can be a polyurethane binder.

In some cases the binder can be curable. That is, the binder can befurther polymerized or cross-linked after the ink is printed onto themedia substrate. In one such example, the binder can include apolymerizable polyurethane. The polymerizable polyurethane can beincluded in the ink in an amount from 1 wt % to 20 wt % in someexamples. In further examples, the polymerizable polyurethane can bewater dispersible and the ink can include an aqueous vehicle.

In certain examples, the polymerizable polyurethane binder can be formedfrom the following components: (a) a diisocyanate (b) a polyol, (c) anacrylate or methacrylate with two or more hydroxyl functional groups,(d) a compound including an ionic group or a group capable of forming anionic group, and (e) another acrylate or methacrylate, the otheracrylate or methacrylate having a hydroxyl functional group or an aminofunctional group. These components can be selected so that the resultingcurable polyurethane binder has a weight average molecular weight (Mw)equal to or less than 5,000, a glass transition temperature (Tg) lessthan 25° C., a double bond density higher than 1.0, and an acid numberranging from 5 to 30.

In addition, the curable polyurethane binder disclosed herein may have aratio of isocyanate groups (NCO) to hydroxyl groups (OH) (i.e., NCO:OHratio) that is greater than 1.8. In another example, the NCO:OH ratio ofthe curable polyurethane binder is equal to or greater than 2.1. In yetanother example, the NCO:OH ratio ranges from about 2.6 to about 2.8. Inthis NCO:OH ratio, it is to be understood that the number of hydroxylgroups (OH) making up the OH portion of the ratio is not the totalnumber of hydroxyl groups in the polyurethane binder, but rather isdetermined from the hydroxyl groups of component (b) (polyol), component(c) (acrylate or methacrylate with two or more hydroxyl functionalgroups), and component (d) (the compound including an ionic group or agroup to form an ionic group). As such, the total number of OH groupsfor the NCO:OH ratio is not based on hydroxyl groups from component (e).While not accounted for in this NCO:OH ratio, it is to be understoodthat the total number of hydroxyl groups (OH) in the polyurethane binderalso includes any hydroxyl groups from component (e).

For component (a), any non-aromatic diisocyanate may be used. In anexample, the non-aromatic diisocyanate may be hexamethylene-1,6-(HDI),2,2,4-trimethyl-hexamethylene-diisocyanate, or a combination thereof.The polyurethane can exclude any other isocyanate. The amount of thenon-aromatic diisocyanate within the curable binder dispersion can rangefrom about 20 wt % to about 50 wt % of the total weight of the curablepolyurethane. In an example, hexamethylene diisocyanate can make up fromabout 30 wt % to about 50 wt % of the polyurethane binder.

Turning to component (b), the amount of component (b) (i.e., the polyol)within the curable polyurethane binder dispersion can range from about10 wt % to about 30 wt % of the total weight of the curablepolyurethane. In an example, component (b) (i.e., the polyol) can makeup from about 15 wt % to about 25 wt % of the polyurethane binder.

Component (b) can be a polyol. The term “polyol”, as used herein, meansany product having an average of about 2 or more hydroxyl groups permolecule. Some examples of suitable polyols for component (b) may bepart of a first class of polyols. As examples, the first class ofpolyols has a number average molecular weight ranging from greater than500 to about 5,000. In any of these examples, component (b) can be amacro-glycol. Examples of suitable polyols of the first class includepolyester polyols, polyether polyols, polycarbonate polyols,poly(ethyleneoxide) polyols, polyhydroxy polyester amides,hydroxyl-containing polycaprolactones, hydroxyl-containing acrylicpolymers, hydroxyl-containing epoxides, polyhydroxy polycarbonates,polyhydroxy polyacetals, polyhydroxy polythioethers, polysiloxanepolyols, ethoxylated polysiloxane polyols, polybutadiene polyols,hydrogenated polybutadiene polyols, polyisobutylene polyols,polyacrylate polyols, halogenated polyesters and polyethers, or mixturesthereof. In an example, the polyol can be poly(propyleneglycol),poly(tetrahydrofuran), poly(ethyleneoxide), a polycarbonate polyol, or apolyester polyol.

Other examples of suitable polyols for component (b) may be part of asecond class of polyols. The second class has a number average molecularweight that is 500 or lower. Examples of suitable polyols of the secondclass include 1,2-propanediol, 1,3-propanediol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,5-pentanediol,3-methylpentane-1,5-diol, 1,6-hexanediol, neopentylglycol,cyclohexane-1,4-dimethanol, 1,2-cyclohexanediol, 1,4-cyclohexanediol,2-ethyl-3-propylpentanediol, 2,4-dimethylpentanediol,2-ethyl-2-butylpropanediol, diethyleneglycol, triethyleneglycol,tetraethyleneglycol, dipropyleneglycol, tripropyleneglycol,N-substituted ethanolamines, and mixtures thereof. In an example, thepolyol is selected from 1,4-butanediol, 1,5-pentanediol,3-methylpentane-1,5-diol, 1,6-hexanediol, neopentylglycol, andcyclohexane-1,4-dimethanol, trimethylolpropane, glycerol, orpentaerythritol.

It is to be understood that a combination of any of the listed polyolsmay be used.

The curable polyurethane binder dispersion may further include component(c). Component (c) includes an acrylate or methacrylate with two or morehydroxyl functional groups. In this example, the acrylate ormethacrylate with two or more hydroxyl functional groups is present inan amount ranging from greater than 0 wt % to about 40 wt % based on thetotal weight of the curable polyurethane.

Some examples of the acrylate or methacrylate with two or more hydroxylfunctional groups include those obtained from the reaction of diglycidylcompounds with (meth)acrylic acid. Aliphatic diglycidyl compoundsderived from alpha, omega diols having 4 to 12 carbon atoms or frompolyoxyalkylenediols (such as polyethylene glycol, polypropylene glycol,or mixtures thereof that contain oxyalkylene groups) may be used. Somespecific examples include 1,4-butanediol diglycidyl ether,1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether,polyethylene glycol diglycidyl ether, polypropylene glycol diglycidylether, hydrogenated bisphenol A diglycidyl ether (BGDA or BADGE),hydrogenated bisphenol F diglycidyl ether, and their ethoxylated and/orpropoxylated equivalents. An additional example is1,6-hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)] bisacrylate. Somecommercially available examples include MIRAMAR™ PE-210 and MIRAMAR™PE-230 (Miwon Chemical).

In further examples, the acrylate or methacrylate with two or morehydroxyl functional groups can include aromatic diglycidyl compoundsderived from bisphenol A and bisphenol F. Specifically, bisphenol Adiglycidyl ether, bisphenol F diglycidyl ether and their ethoxylatedand/or propoxylated equivalents may be used. Diglycidyl esters may alsobe used, such as diglycidyl phthalate, N,N-diglycidyl aniline, orN,N-diglycidyl-4-glycidyloxyaniline. Some specific examples include adiacrylate ester of bisphenol A diglycidyl ether (BGDA) and adimethacrylate ester of bisphenol A diglycidyl ether (BGDM).

Component (d) is a compound including an ionic group or a group that iscapable of forming an ionic group. The amount of component (d) withinthe curable binder dispersion ranges from greater than 0 wt % to about10 wt % based upon the total weight of the curable polyurethane. In anexample, component (d) makes up from about 2 wt % to about 6 wt % of thepolyurethane binder.

The presence of component (d) assists in the ability of the polyurethaneto be dissolved or dispersed in water after ionization with a base.Examples of component (d) may be derived from hydroxy-carboxylic acidshaving the general formula (HO)xQ(COOH)y, where Q is a straight orbranched hydrocarbon radical containing 1 to 12 carbon atoms, and x andy each independently range from 1 to 3. Examples of suitablehydroxy-carboxylic acids include dimethylol propionic acid (DMPA),dimethylol butanoic acid (DMBA), citric acid, tartaric acid, glycolicacid, lactic acid, malic acid, dihydroxymaleic acid, dihydroxytartaricacid, or mixtures thereof. Hydroxyls or amines containing a sulfonatefunctional group can also be used as component (d). Examples includetaurine and aminoethylaminopropylsulfonate (EPS). Hydroxyls or aminescontaining a phosphate functional group can also be used as component(d). An example includes glycerol phosphate disodium dehydrate.

Turning now to component (e), component (e) is an acrylate ormethacrylate having a hydroxyl functional group or an amino functionalgroup. The amount of component (e) in the curable polyurethane binderdispersion can range from greater than 10 wt % to about 65 wt % basedupon the total weight of the curable polyurethane. In an example,component (e) makes up from about 20 wt % to about 50 wt % of thepolyurethane binder.

Some examples of component (e) include the esterification products ofaliphatic and/or aromatic polyols with acrylic acid or methacrylic acid.These products have a residual OH functionality of about 1. Some ofthese products also have two or more acrylic functionalities. Examplesof component (e) include the partial esterification products of acrylicacid or methacrylic acid with tri-, tetra-, penta- or hexahydric polyolsor mixtures thereof. These modified or unmodified polyols are partlyesterified with acrylic acid, methacrylic acid or mixtures thereof untilthe desired residual hydroxyl functionality is reached. Suitableexamples include acrylic or the methacrylic esters with linear andbranched polyols in which the one or more hydroxyl functionality remainsfree, such as hydroxyalkylacrylates or hydroxyalkylmethacrylates having1 to 20 carbon atoms in the alkyl group. Some specific examples includehydroxyethylacrylate (HEA), hydroxyethylmethacrylate (HEMA),hydroxybutylacrylate (HBA), hydroxybutylmethacrylate (HBMA),(3-(acryloxy)-2-hydroxypropylmethacrylate) (AHPMA), glycerol diacrylate,trimethylolpropane diacrylate, pentaerythritoltriacrylate (PETA),ditrimethylolpropane triacrylate (DTPTA), dipentaerythritolpentaacrylate (DPPA), and (poly)ethoxylated and/or (poly)propoxylatedequivalents of glycerol diacrylate, trimethylolpropane diacrylate, PETA,DTPTA, or DPPA.

The ink used in the printing systems described herein can also includemonomers that can be polymerized by exposure to radicals or otherspecies generated by the plasma generator. In some examples, suchpolymerizable monomers can be used in addition to a polymerizablepolyurethane dispersion as described above. In other examples, the inkcan include polymerizable monomers without the polymerizablepolyurethane dispersions described above.

In some examples, the ink can include polymerizable monomers that arehydrophobic. In certain examples, the polymerizable monomers can beacrylate monomers, vinyl monomers, or combinations thereof. Examples ofacrylate monomers can include 2-phenoxyethyl acrylate, isophorylacrylate, isodecyl acrylate, tridecyl acrylate, lauryl acrylate,2-(2-ethoxy-ethoxy)ethyl acrylate, tetrahydrofurfuryl acrylate,isobornyl acrylate, propoxylated acrylate, tetrahydrofurfurylmethacrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate andcombinations thereof. Examples of vinyl monomers can include vinylcaprolactam, vinyl ether and any combinations thereof.

In certain examples, the polymerizable monomer can include vinylcaprolactams, hexanediol diacrylates, trimethylolpropane triacrylates,propoxylated neopentyl glycol diacrylates, ethoxylated bisphenol Adiacrylate, tris(2-hydroxyethyl) isocyanurate triacrylate, orcombinations thereof.

In further examples, the polymerizable monomers can be water-soluble orwater-miscible. In some examples, the monomers can include esters ofacrylic or methacrylic acid with polyethylene glycol or with a mono-,di-, tri- or tetra-hydric alcohol derived by ethoxylating a mono-, di,tri- or tetra-hydric aliphatic alcohol of molecular weight less than 200with ethylene oxide. In further examples, the monomers can includeacrylate esters of polyethylene glycols made from a polyethylene glycolhaving a molecular weight of from about 200 to about 1500, or from about400 to about 800; or acrylic esters of ethoxylated trimethylolpropane,having from 9 to 30 ethoxylate residues, or from 10 to 20 ethoxylateresidues. Other examples can include acrylate esters of polyethyleneglycols made from a polyethylene glycol having a molecular weight offrom about 200 to about 1500 and acrylic esters of ethoxylatedtrimethylolpropane having from 9 to 30 ethoxylate residues.

Still further examples of the polymerizable monomers can includepolyethylene glycol (600) diacrylate, polyethylene glycol (400)diacrylate, methoxy polyethylene glycol (550) mono-acrylate,polyethylene glycol (6) mono-acrylate, 30 ethoxylated bisphenol-Adiacrylate, ethoxylated (20) trimethylopropane-triacrylate, (15)ethoxylated trimethylopropane-triacrylate, tris-tryl phenol 18eoacrylate, glycerol 12eo triacrylate, and combinations thereof. In otherexamples, the monomers can be ethoxylated tri-methylpropanetriacrylates.

Examples of suitable commercially available materials can include thefollowing UV-curable materials available from Sartomer such SR415®(ethoxylated (20) trimethylolpropane-triacrylate), CN435® or SR9015®.Other examples of commercially available water-soluble or dispersiblemonomers include: CD5500® (methoxy polyethylene glycol (350)mono-methacrylate), CD552® (methoxy polyethylene glycol (550)mono-methacrylate), SR259® (polyethylene glycol (200) diacrylate),SR344® (polyethylene glycol (400) diacrylate), SR603® (polyethyleneglycol (400) di-methacrylate), SR610® (polyethylene glycol (600)diacrylate), SR252® (polyethylene glycol (600) di-methacrylate), SR604®(polypropylene glycol mono-methacrylate, SR256® (2-(2-ethoxyethoxy)ethylacrylate), SR9035 (ethoxylated(15)trimethylolpropane triacrylate), allavailable from Sartomer; Ebecryl®11 (polyethylene glycol diacrylate),and Ebecryl®12 (polyether triacrylate) available from UCB; Genomer®1251(polyethylene glycol 400 diacrylate), Genomer®1343 (ethoxylatedtrimethylolpropane triacrylate), Genomer® 1348 (glycerol-propoxytriacrylate), Genomer®1456 (polyether polyol tetra-acrylate), anddiluent 02-645 (ethoxy ethyl acrylate), all available from Rahn.

In still further examples, the monomers can include acrylamidesmonomers. Representative and non-limiting examples of acrylamidewater-soluble or water-miscible monomers include N-(2-hydroxyethyl)acrylamide; N,N′-methylene bis-acrylamides and/or N-isopropylacrylamides. Commercially available water-soluble or dispersiblemonomers include, for examples, Flocryl®MBA available from SNF FLOERGER(France); Jarchem®HEAA or Jarchem®NIPAM both available from Jarchem(USA, N.J.).

The ink can further be devoid or substantially devoid ofphotoinitiators. Because the plasma generator is used to cure the ink,no UV radiation is necessary to cure the ink. Accordingly, the ink doesnot need to include a photoinitiator. Eliminating the photoinitiatorfrom the ink can provide advantages such as making the ink more stable,increasing the shelf-life of the ink, and so on. Inks that containcurable components and photoinitiators can often undergo prematurepolymerization if exposed to UV light. Additionally, manyphotoinitiators are difficult to disperse or dissolve in aqueous inkvehicles. However, the present technology allows for the use of curableink without a photoinitiator. Therefore, these problems can be avoided.

The ink used in the printing systems described herein can also include aliquid vehicle. In some examples, liquid vehicle formulations that canbe used in the ink can include water and one or more co-solvents. Theco-solvents can be present in total at from 1 wt % to 50 wt %, dependingon the jetting architecture. Further, one or more non-ionic, cationic,and/or anionic surfactants can be present, ranging from 0.01 wt % to 20wt % (if present). In one example, the surfactant can be present in anamount from 0.1 wt % to 20 wt %. The liquid vehicle can also includedispersants in an amount from 0.1 wt % to 20 wt %. The balance of theformulation can be purified water, or other vehicle components such asbiocides, viscosity modifiers, materials for pH adjustment, sequesteringagents, preservatives, and the like. In one example, the liquid vehiclecan be more than 50 wt % water.

In further examples, the liquid vehicle can be a non-aqueous,solvent-based vehicle. In one example, the liquid vehicle can includeethanol and additional co-solvents. Classes of co-solvents that can beused can include organic co-solvents including aliphatic alcohols,aromatic alcohols, diols, glycol ethers, polyglycol ethers,caprolactams, formamides, acetamides, and long chain alcohols. Examplesof such compounds include primary aliphatic alcohols, secondaryaliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethyleneglycol alkyl ethers, propylene glycol alkyl ethers, higher homologs(C₆-C₁₂) of polyethylene glycol alkyl ethers, N-alkyl caprolactams,unsubstituted caprolactams, both substituted and unsubstitutedformamides, both substituted and unsubstituted acetamides, and the like.Specific examples of solvents that can be used include, but are notlimited to, 2-pyrrolidinone, N-methylpyrrolidone,2-hydroxyethyl-2-pyrrolidone, 2-methyl-1,3-propanediol, tetraethyleneglycol, 1,6-hexanediol, 1,5-hexanediol and 1,5-pentanediol.

Surfactants that can be included in the ink can include alkylpolyethylene oxides, alkyl phenyl polyethylene oxides, polyethyleneoxide block copolymers, acetylenic polyethylene oxides, polyethyleneoxide (di)esters, polyethylene oxide amines, protonated polyethyleneoxide amines, protonated polyethylene oxide amides, dimethiconecopolyols, substituted amine oxides, and the like. Suitable surfactantscan include, but are not limited to, liponic esters such as Tergitol™15-S-12, Tergitol™ 15-S-7 available from Dow Chemical Company, LEG-1 andLEG-7; Triton™ X-100; Triton™ X-405 available from Dow Chemical Company;LEG-1, and sodium dodecylsulfate.

Various other additives may be employed to enhance the properties of theink composition for specific applications. Examples of these additivesare those added to inhibit the growth of harmful microorganisms. Theseadditives may be biocides, fungicides, and other microbial agents, whichare routinely used in ink formulations. Examples of suitable microbialagents include, but are not limited to, NUOSEPT® (Nudex, Inc.),UCARCIDE™ (Union carbide Corp.), VANCIDE® (R. T. Vanderbilt Co.),PROXEL® (ICI America), ACTICIDE® (Thor Specialties Inc.) andcombinations thereof. Sequestering agents such as EDTA(ethylenediaminetetraaceticacid) may be included to eliminate thedeleterious effects of heavy metal impurities. From 0.001% to 2.0% byweight, for example, can be used. Viscosity modifiers may also bepresent, as well as other additives known to those skilled in the art tomodify properties of the ink as desired. Such additives can be presentat from 0.01% to 20% by weight.

In some examples, the inkjet ink can include ingredients in the amountslisted in Table 1:

TABLE 1 Component Weight Percent Binder 0.5-10% Biocide   0-5%Surfactant  0-10% Anti-kogation agent   0-5% Colorant 0.5-10% OrganicCo-solvent 0.1-50% Water* Balance *Note that by “balance,” what is meantis that water is used to achieve 100 wt %. Other ingredients other thanthe ones shown in Table 1 may be present, and water is used to arrive at100 wt %, regardless of what other ingredients are present.

The media substrate used in the printing system can be any of a widevariety of media substrates. Because the printing system includes thepretreatment head with the first plasma generator to pretreat the mediasubstrate before printing, the media substrate may or may not includefixer or other special ingredients to make the media substrate morecompatible with inkjet inks. In one example, the media substrate can besubstantially devoid of fixer. In another example, the media substratecan include calcium carbonate. Calcium carbonate does not act as afixer, but the calcium carbonate can be converted into calcium cationsby the plasma treatment, or can otherwise interact with the plasma toimprove image quality. The plasma treatment can also be used on paperspecially manufactured for inkjet printing. The plasma treatment canpotentially further improve the print quality using such paper. Invarious further examples, the media substrate can be plain paper, photopaper, glossy paper, offset paper, coated paper, textile, orcombinations thereof.

The present disclosure also includes methods of forming a printed imageon a media substrate. FIG. 5 shows one example of a method 500 offorming a printed image on a media substrate. The method includes plasmatreating a surface of a media substrate 510; jetting an inkjet ink froman inkjet print head onto the pretreated surface of the media substrateto form a printed image on the media substrate 520; and plasma treatingthe printed image after printing 530.

In some examples, the inkjet ink jetted onto the media substrate can bea pigment-based ink. The ink can include an anionically dispersedpigment, which can interact with the pretreated surface of the mediasubstrate. The cationic species and/or oxygen containing groups on thepretreated surface of the media substrate can cause the anionicallydispersed pigment to become destabilized or to “crash out” of solutionin the ink. The pigment can then be immobilized at the surface of themedia substrate while the liquid vehicle and other components of the inkcan be absorbed into the media substrate. This can result in a higheroptical density and color saturation compared to printing on a mediasubstrate that has not been pretreated with the plasma treatment. Insome examples, the media substrate can be substantially devoid of fixer.Thus, the optical density and color saturation achieved by printing onthe plasma treated media substrate can be significantly improvedcompared to printing on an untreated media substrate

In various examples, the plasma pretreatment and/or post-treatment canbe performed with a surface barrier discharge plasma generator at adistance from the media substrate up to 10 mm away from the mediasubstrate. For example, the distance between the plasma generator andthe media substrate can be small enough that the media substrate passesthrough the plasma arcs generated by the plasma generator. However, inother examples the distance can be greater than the depth of the plasmaarcs so that the plasma arcs are located above the surface of the mediasubstrate.

In further examples, the plasma pretreatment can be performed for a timeperiod of 0.1 second to 20 seconds. In more specific examples, thepretreatment time period can be 0.2 second to 10 seconds or 0.5 secondto 5 seconds. In still further examples, the plasma post-treatment canbe performed for a time period of 1 second to 20 seconds. In morespecific examples, the time period can be 2 second to 10 seconds or 2second to 5 seconds. As used herein, the time period of the plasmatreatments refers to the amount of time that a treated portion of themedia substrate is exposed to the plasma. As explained above, the mediasubstrate may be in direct contact with the plasma arc or merely havethe plasma arc passed over the media substrate. In the case of a web-fedprinting system, the media substrate can constantly move past thesurface barrier discharge plasma generator. Thus, the time period of theplasma treatment can be the time required for a point on the mediasubstrate to travel across the length of the plasma generator. Inexamples where the printing system includes the plasma generator on acarriage, the plasma generator can either be held stationary over aportion of the media substrate for the plasma treatment time period, orthe carriage can move at an appropriate speed so that each portion ofthe media substrate is plasma treated for the appropriate time period.

Generally, longer pretreatment time periods can provide better printingresults, as signified by higher optical density and color saturation.However, in some examples a maximum effect can be reached after acertain time period. This time period can be from 0.1 second to 20seconds or any of the other time periods described above. In furtherexamples, the distance of the plasma generator from the media substratecan affect the time period required to reach the maximum pretreatmenteffect. At greater distances, a longer time period may be required.

Additionally, longer plasma post-treatment can provide better durabilityof curable ink. In further examples, the distance of the plasmagenerator from the media substrate can affect the time period requiredto reach a given level of durability. At greater distances, a longertime period may be required.

The present disclosure also includes printed articles made using thesystems and methods described herein. FIG. 6 shows one example of aprinted article 600. The printed article includes a media substrate 620.The media substrate includes a surface 645 that has been modified by aplasma generator before printing to form cationic species, oxygencontaining groups, or a combination thereof on the surface. A printedimage is formed on the media substrate. The printed image includes aninkjet ink that has been cured by a plasma treatment. In particular, theprinted image includes pigment particles 635 in contact with the surfaceof the media substrate and a polymerized binder 625 over and throughoutthe pigment particles. The polymerized binder can be a polymerizedpolyurethane dispersion that has been cross-linked by exposure to freeradicals generated by the plasma generator. Additionally, the ink in theprinted image can be substantially devoid of photoinitiators.

FIG. 7 shows another example of a printed article 700. The printedarticle includes a media substrate 720 having a surface 745 modified bya plasma generator before printing to form cationic species, oxygencontaining groups, or a combination thereof on the surface. A printedimage is formed by jetting an inkjet ink on the modified surface of themedia substrate. The printed image includes pigment particles 735 incontact with the modified surface of the media substrate and apolymerized binder 725 on and throughout the pigment particles. Anovercoat layer 755 is coated over the printed image. The overcoat layercan include a polymerizable component that has been polymerized byexposure to the free radicals generated by the second plasma generator.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe content clearly dictates otherwise.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andcan be determined based on experience and the associated descriptionherein.

In this disclosure, “comprises,” “comprising,” “having,” “includes,”“including,” and the like, and are generally interpreted to be openended terms. The term “consisting of” is a closed term, and includesonly the methods, compositions, components, steps, or the likespecifically listed. “Consisting essentially of” or “consistsessentially” or the like, when applied to methods, compositions,components, steps, or the like encompassed by the present disclosure,refers to elements like those disclosed herein, but which may containadditional composition components, method steps, etc., that do notmaterially affect the basic and novel characteristic(s) of thecompositions, methods, etc., compared to those of the correspondingcompositions, methods, etc., disclosed herein. When using an open endedterm, like “comprising” or “including,” it is understood that directsupport should be afforded also to “consisting essentially of” languageas well as “consisting of” language as if stated explicitly, and viceversa.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, dimensions, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, a weight ratio range of about 1 wt % to about 20 wt % should beinterpreted to include not only the explicitly recited limits of 1 wt %and about 20 wt %, but also to include individual weights such as 2 wt%, 11 wt %, 14 wt %, and sub-ranges such as 10 wt % to 20 wt %, 5 wt %to 15 wt %, etc.

Percentages, ratios, and parts refer to weight percentages, weightratios, and parts by weight unless otherwise specified or otherwiseclear from the surrounding context.

As a further note, in the present disclosure, it is noted that whendiscussing the printing systems, methods of forming a printed image, andprinted articles, each of these discussions can be considered applicableto each of these examples, whether or not they are explicitly discussedin the context of that example. Thus, for example, in discussing detailsabout the printing system per se, such discussion also refers to themethods and the printed articles described herein, and vice versa.

The following examples illustrate aspects of the present technology.However, it is to be understood that these examples are only exemplaryor illustrative of the application of the principles of the presentsystems and methods. Numerous modifications and alternative systems,methods, compositions, media, and so on may be used without departingfrom the spirit and scope of the present disclosure. The appended claimsare intended to cover such modifications and arrangements. Thus, whilethe technology has been described with particularity, the followingexamples provide further detail in connection with the presenttechnology.

EXAMPLES Example 1 Pretreatment

A surface barrier discharge plasma generator was used to treat a mediasubstrate. The plasma generator was model RPS40 from ROPLASS S.R.O. Thisplasma generator has the following specifications:

TABLE 2 ROPLASS RPS40 Specifications Power (W) 40 Plasma Area (cm²) 7.5Plasma Depth (cm) 0.03 Frequency (kHz) 25 Voltage (kV, peak to peak) 15

A blank sheet of white paper (Hammermill GW30) was treated with theplasma generator for 5 seconds at a distance of 1 mm. After the plasmatreatment, a 50% area fill of cyan ink (HP PageWide XL® cyan ink fromHewlett Packard) was printed across the treated and untreated areas.Color saturation, defined as chroma divided by L*, was then measured inthe treated area and the untreated area. Color saturation was measuredusing a GretagMacbeth Spectrolino™ CH9105 color measurement device usingD65 illuminant at 2 degrees observer angle and reflectance mode. Theuntreated area had a color saturation of 0.71 and the treated area had acolor saturation of 1.03, which is about a 45% increase in colorsaturation.

This test was repeated with another sheet of Hammermill GW30 and amagenta ink (HP PageWide XL® magenta ink from Hewlett Packard). Theplasma treatment was performed for the same time period at the samedistance. After the plasma treatment, a 50% area fill of the magenta inkwas printed across the treated and untreated areas. The untreated areahad a color saturation of 0.96 and the treated area had a colorsaturation of 1.52, which is about a 58% increase in color saturation.

Example 2 Post-Treatment

A curable ink was formulated by mixing a curable polyurethane dispersioninto HP PageWide XL ink at an amount of 5 wt % with respect to theentire weight of the ink. This ink did not contain a photoinitiator. Theink was printed onto Sterling® Ultragloss media using an inkjet printingsystem. An area of the printed ink was then cured using the ROPLASSRPS40 plasma generator at a height of 1 mm for 5 seconds. Forcomparison, another area was left untreated.

The treated and untreated areas were tested by finger rubbing with a wetTexwipe® wipe. The treated area showed very little smudging, while theuntreated area showed significant smudging. These results show that theplasma treatment can cure the curable polyurethane in the ink withoutthe presence of a photoinitiator

Example 3 Combined Pretreatment and Post-Treatment

A blank sheet of white paper is pretreated using a surface barrierdischarge plasma generator as described in Example 1. Afterpretreatment, a curable ink is printed on the paper and the ink is curedusing a surface barrier discharge plasma generator as described inExample 2. The final printed image has improved color saturation anddurability.

While the disclosure has been described with reference to certainexamples, various modifications, changes, omissions, and substitutionscan be made without departing from the spirit of the disclosure. It isintended, therefore, that the disclosure be limited only by the scope ofthe following claims.

What is claimed is:
 1. A printing system, comprising: a pretreatmenthead comprising a first plasma generator to apply a plasma treatment toa media substrate; an inkjet print head positioned with respect to thepretreatment head to form a printed image on the media substrate afterthe plasma treatment; and a post-treatment head comprising a secondplasma generator positioned with respect to the inkjet print head totreat the printed image on the media substrate.
 2. The printing systemof claim 1, wherein one or both of the first plasma generator and secondplasma generator is a surface barrier discharge plasma generator.
 3. Theprinting system of claim 1, further comprising the media substrate,wherein the media substrate is media web that is web fed, and whereinthe pretreatment head and the post-treatment head are independently 75%or more as wide as the media web.
 4. The printing system of claim 1,further comprising the media substrate, wherein the media substrate is apaper that is substantially devoid of fixer.
 5. The printing system ofclaim 1, further comprising an ink reservoir in fluid communication withthe inkjet print head, the ink reservoir comprising a pigment-basedinkjet ink, wherein the pigment-based inkjet ink comprises an anionicpigment.
 6. The printing system of claim 5, wherein the pigment-basedinkjet ink further comprises a polymerizable component capable ofpolymerizing upon exposure to free radicals.
 7. The printing system ofclaim 6, wherein the polymerizable component is a polymerizable monomer,a polymerizable polyurethane dispersion comprising functional groupsthat cross-link upon exposure to free radicals, or combinations thereof.8. The printing system of claim 5, wherein the pigment-based ink issubstantially devoid of photoinitiators.
 9. The printing system of claim1, wherein the post-treatment head further comprises an injector toinject a polymerizable overcoat composition into plasma generated by thesecond plasma generator.
 10. A method of forming a printed image on amedia substrate, comprising: plasma treating a surface of a mediasubstrate; jetting an inkjet ink from an inkjet print head onto thepretreated surface of the media substrate to form a printed image on themedia substrate; and plasma treating the printed image after printing.11. The method of claim 10, wherein one or both of plasma treating thesurface of the media substrate and plasma treating the printed image isperformed utilizing a surface barrier discharge plasma generator. 12.The method of claim 10, further comprising injecting a polymerizableovercoat composition into plasma generated to plasma treat the printedimage.
 13. The method of claim 10, wherein plasma treating the surfaceof the media substrate and plasma treating the printed image areindependently performed for a time period of 0.1 second to 20 seconds.14. A printed article, comprising: a media substrate having a surfacemodified by a first plasma generator to form cationic species, oxygencontaining groups, or a combination thereof on the surface; and aprinted image formed by jetting an inkjet ink on the modified surface ofthe media substrate, wherein the printed image comprises pigmentparticles in contact with the modified surface of the media substrate,and wherein the inkjet ink comprises a polyurethane dispersion that hasbeen cross-linked by exposure to free radicals generated by a secondplasma generator.
 15. The printed article of claim 14, furthercomprising an overcoat layer over the printed image, wherein theovercoat layer comprises a polymerizable component that has beenpolymerized by exposure to the free radicals generated by the secondplasma generator.